Denis M. Gokhfeld

Bean formula is widely used to estimate the critical current density Jc from magnetization hysteresis loops. However, when the local critical current density decreases with magnetic field, the Bean estimate at zero field, Jc,Bean(0), is systematically lower than the true value jc0 of the critical current density. To overcome this underestimate, a correction term is suggested for refining the zero-field critical current density Jc(0). The accuracy of several simple combinations of characteristic magnetization values is evaluated by the root-mean-square deviation of the computed values of Jc(0) from jc0 for 100 loops computed with varied parameters. The most accurate formula Jc(0) = Jc,Bean(0) M–(Hmin)/M0(Hmin0) requires only two additional readings, taken at the minima on the initial magnetization branch and the envelop branch of the magnetization hysteresis loop. This formula also performs well for asymmetric magnetization hysteresis loops containing an equilibrium-magnetization contribution. Application of the proposed formula to experimental data for a (Y,Gd)BCO polycrystalline sample and a SmBCO single crystal gives the critical current density 1.23 and 1.45 times larger, respectively, than the Bean estimates.

On July 21, 2026, Mikhail Ivanovich Petrov, a senior researcher at the Laboratory of High Magnetic Fields, Kirensky Institute of Physics, passed away. Petrov was a pioneer and organizer of experimental research of high-temperature superconductivity at the institute. This article briefly describes his scientific career and cites several of his works on superconducting composites, porous superconductors, large-grain superconductors, and doping of superconducting materials.

The influence of adding 23 nm NiO nanoparticles on the magnetic hysteresis loops and critical current density of the high-temperature superconductor YBa2Cu3O7-d has been investigated. The samples were prepared using a fast annealing method that prevents chemical interaction between the components and does not reduce the critical temperature of the superconductor. Compared to the undoped YBCO sample, the critical current density increases in the samples doped with NiO nanoparticles in magnetic fields greater than 6 kOe. The sample containing 0.5 weight percent of NiO nanoparticles exhibits the greatest enhancement in critical current density at 10 kOe (1.36 times greater than the undoped sample).

A recent study, “Revealing the vortex phases and second magnetization peaks in SmBCO superconductors” published in J. Appl. Phys. 136 (2024), presents detailed resistance and magnetization measurements of a single-crystal Sm-based high-Tc superconductor at different temperatures and magnetic fields. Based on these measurements, the authors constructed the vortex phase diagram and discussed the pinning mechanism. Due to the significance of this research area, clarifications concerning pinning force curves Fp(H) estimated from magnetization hysteresis loops must be addressed. A peak located near the highest applied field does not necessarily demonstrate the maximal pinning force. The peak position only corresponds to the maximal pinning force when the highest applied field is close to or greater than the irreversibility field Hirr.

The determination of the critical current density from magnetic hysteresis loops is widely used to characterize and compare superconducting samples. For tapes and single crystals, magnetic hysteresis loops depend on both the critical current density and the sample size, which determine the scale of supercurrent circulation. However, in polycrystalline hightemperature superconductors prepared by solid-phase synthesis or the sol-gel method, the magnetization is determined by the circulation of supercurrents in the granules. The effect of the granule size distribution on the effective scale of current circulation is discussed in the paper. The log-normal distribution and the Weibull distribution are considered. The effective size for estimating the intragranular critical current density can be significantly larger than the average granule size.

The effect of the Mn3+ ion on the local distortions of the FeO6 octahedra in orthoferrite samples was investigated. Mössbauer spectroscopy measurements for a series of the HoFe1−xMnxO3 (x=0.0−0.7) orthoferrite samples with space group Pnma was carried out at temperatures above the Néel point (700 K). The electric field gradient (EFG) tensor on Fe ions for these compounds was found using the first-principle calculations. The concentration dependence of the quadrupole splitting was resulted from the experimental and theoretical data. The absence of an electron contribution to the quadrupole splitting at all the manganese concentrations was demonstrated. It was shown by the theoretical calculations that the values of all the electric field gradient components increase significantly with the manganese concentration in the system, and the eigenvectors Vxx and Vyy of the electric field gradient tensor sharply change their direction at concentrations of x > 0.1.